1. Field of the Invention
The present invention relates to a micro movable mechanism system and a control method for the same. More specifically, the present invention relates to a micro movable mechanism system such as a Micro-Electro-Mechanical System (MEMS) mirror system and a control method for the same.
2. Description of Related Art
Optical communication is carried out by transmitting and receiving light signals through optical transmission lines formed by optical fibers. In the optical communication in practice, the light signals need to be switched between a plurality of optical transmission lines. For this purpose, an optical switch is used to directly switch the light signal to a selected one of the plurality of optical transmission lines.
An optical switch is shown in Japanese Laid Open Patent Application (JP-2000-19434A). The optical switch of the conventional example is composed of an input side optical transmission line and a plurality of output side optical transmission lines. A movable reflection surface reflects the light signal emitted from the input side transmission line to a selected one of the plurality of output side optical transmission lines, which is selected by controlling the reflection surface of the optical switch by a control unit.
A micro machine is shown in Japanese Patent No. 2682181 as an actuator controlling the reflective surface of such an optical switch. In the micro machine, a drive voltage is applied to a fixed electrode to move a movable electrode by electrostatic force. An angle of the moving mobile electrode is determined based on the balance of the electrostatic force and spring stiffness. Therefore, in order to turn the movable electrode to an optional angle, some methods are proposed such as: an open loop control method in which a drive voltage corresponding to a target angle is applied, a feeding-back method in which the warp of the spring is detected and the angle is detected, as shown in U.S. Pat. No. 6,392,220, and a feeding-back control method in which feeding-back control is carried out based on light intensity as shown in U.S. Pat. No. 6,301,402.
The light switch moves the reflection surface in the controllable range of a control unit. With the light switch, it is demanded to expand a controllable angle range of the reflection surface, while keeping a shorter switching time and higher angle precision. Also, it is demanded to increase the number of ports for the light signal to be switched to.
Also, referring to FIG. 26, the relation of the angle of the movable electrode and the electrostatic force generated based on the drive voltage is not linear (a constant ratio). Especially, a difference from the linear relation becomes larger as the angle becomes larger. Consequently, if the movable electrode is moved to a larger angle using a linear control unit for the feedback control, over-shoot occurs in the angle of the movable electrode, as shown in FIG. 27. The over-shoot elongates the switching time. Therefore, it is demanded that the switching time of the light switch can be reduced.
In conjunction with the above description, a controller is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 6-282305). The controller controls a nonlinear mechanical system which has a plurality of degrees of freedom. The controller is composed of a subtractor which subtracts an output signal of the mechanical system from a preset point signal. A compensation section inputs the output signal of the subtractor as an input signal of a control unit, and compensates a nonlinear operation of the mechanical system. An adder adds an output signal of the compensation section and an output signal of the control unit. Reference models of the control unit and the linearized mechanical system inputs an output signal of the adder as an input signal of the mechanical system. An adaptable section inputs the preset point signal as the input signal of the reference models and adaptively control the compensation section in accordance with the difference between the output signal of the mechanical system and the output signal of the reference models.
Also, a control system of an actuator which has a nonlinear element is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-23777). The control system controls the actuator which has inertia large relatively to a torque constant and in which internal variables such as the torque constant changes in accordance with a turned position. By comparing an drive current value of a motor as a driving source of the actuator and angular acceleration, a deviation quantity of motor drive control from linear control is measured using a relation of current and torque in real time. Thus, external torque observer control is carried out to correct a motor control system. The control system is composed of an oscillation prevention filter for the current drive of the motor, a filter provided in a differentiator attachment and used to calculate angular velocity from a position sensor output to the motor, a filter used to calculate angular acceleration from the angular velocity, a filter provided in a position signal inputting section and used for noise removal, and a noise removal filter which contains a filter after the difference between the current and the angular acceleration is calculated. The noise removal filter has the lowest frequency range.
Also, a servo control method of a nonlinear mechanism is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-85285). In the servo control method, a nonlinear mechanism is controlled in which a ratio of a angular position of a drive motor and a movement quantity of a target to be controlled is controlled. A position instruction is supplied to the servo control unit. A loop gain in a feedback loop of a servo control apparatus is changed in accordance with the rotation angle of the drive motor. Thus, a characteristic can be obtained which is equivalent to the characteristic when a linear mechanism having a constant relation of the rotation angle of the motor and a movement quantity of an object.
Also, a vibration body apparatus is disclosed in Japanese Laid Open Patent Application (JP-P2000-314846A). A space is connected to an external space by providing a penetrating hole for the surface of the substrate opposing to the vibration body to support a mirror. A compressed air generated through the vibration of the vibration body is controlled by providing a mesh electrode and butterfly valve which operate in relation to the operation of the vibration body. The vibration body is prevented from adhering by introducing air into the space through the penetrating hole.
Also, a drive circuit of an electromagnetic drive light scan apparatus is disclosed in Japanese Laid Open Patent Application (JP-P2001-91890A). The drive circuit supplies alternating current for driving a movable board to a coil of the electromagnetic driven light scan apparatus which is composed of a mirror and the coil provided for the surface of the movable board which is turnably supported through a torsion bar, and a magnetic field generating section which generates a magnetic field such that the magnetic field acts on a part of the coil parallel to an axial direction of the torsion bar. The drive circuit is composed of a drive signal generating section for generating a pair of complementary drive signals with a predetermined frequency, a current conversion section for converting DC current into AC current in accordance with the drive signals to supply to the coil, a current detection section for detecting an actual current value which flows through the coil, an angle setting section for setting an angle of the movable board, a current value setting section for setting the drive current value of the movable board such that the angle of the movable board is equal to the set angle, and a current control section for comparing the set current value and the detected current value and for controlling the DC current value supplied to the current conversion section such that the detected current value is equal to the set current value.
Also, a micro movable mechanism is disclosed in Japan Patent No. 2682181. In the micro movable mechanism, a movable electrode is driven in accordance with electrostatic force generated voltage applied to a fixed electrode. One of the movable electrode and the fixed electrode is formed of a single crystal semiconductor which has an uneven shape in a position opposing to the other. The movable electrode or the fixed electrode is formed on a semiconductor substrate, and then the formed electrode is transferred to another substrate.